diff --git a/CHANGELOG.md b/CHANGELOG.md
index aebf6f0fd5..4146423c9d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,7 +22,7 @@
 - Fix: オブジェクトストレージの設定でPrefixを設定していなかった場合nullまたは空文字になる問題を修正
 - Fix: pgroongaでの検索時にはじめのキーワードのみが検索に使用される問題を修正  
   (Cherry-picked from https://activitypub.software/TransFem-org/Sharkey/-/merge_requests/886)
-
+- Fix: メールアドレスの形式が正しくなければ以降の処理を行わないように
 
 ## 2025.2.0
 
diff --git a/packages/backend/src/core/EmailService.ts b/packages/backend/src/core/EmailService.ts
index da198d0e42..45d7ea11e4 100644
--- a/packages/backend/src/core/EmailService.ts
+++ b/packages/backend/src/core/EmailService.ts
@@ -164,6 +164,13 @@ export class EmailService {
 		available: boolean;
 		reason: null | 'used' | 'format' | 'disposable' | 'mx' | 'smtp' | 'banned' | 'network' | 'blacklist';
 	}> {
+		if (!this.utilityService.validateEmailFormat(emailAddress)) {
+			return {
+				available: false,
+				reason: 'format',
+			};
+		}
+
 		const exist = await this.userProfilesRepository.countBy({
 			emailVerified: true,
 			email: emailAddress,
diff --git a/packages/backend/src/core/UtilityService.ts b/packages/backend/src/core/UtilityService.ts
index fcb750d3bf..23fb928ac9 100644
--- a/packages/backend/src/core/UtilityService.ts
+++ b/packages/backend/src/core/UtilityService.ts
@@ -38,6 +38,14 @@ export class UtilityService {
 		return this.punyHost(uri) === this.toPuny(this.config.host);
 	}
 
+	// メールアドレスのバリデーションを行う
+	// https://html.spec.whatwg.org/multipage/input.html#valid-e-mail-address
+	@bindThis
+	public validateEmailFormat(email: string): boolean {
+		const regexp = /^[a-zA-Z0-9.!#$%&'*+\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/;
+		return regexp.test(email);
+	}
+
 	@bindThis
 	public isBlockedHost(blockedHosts: string[], host: string | null): boolean {
 		if (host == null) return false;